1. Field of the Invention
The present invention relates to a door closer with a door piston, which door piston acts on a driven shaft and has an extension, a pressure piston and an energy storage mechanism which acts on the pressure piston. The pistons can be axially guided and can interact with hydraulically connected pressure chambers to connect and disconnect the pistons during the opening and closing of the door closer.
2. Background Information
Swedish Patent No. 469 342 B discloses a door closer in which a closing moment characteristic adapted to the door angle is achieved by first stretching or applying tension to a first spring which acts on the door piston, and then in series or sequence to a second spring which acts on a pressure piston or plunger or ram. When the door closes, first the spring which acts on the door piston transmits its energy, whereby the second spring remains in the stretched position until a slide which is mounted centrally in both pistons hydraulically relieves the pressure via a system of channels which keeps the pressure piston pressurized, so that the second spring can then give up its energy to the driven shaft.
Although this door closer is capable of exerting different moments on the door as a function of the opening of the door, it is extraordinarily expensive to manufacture.
In particular, it requires extremely precise and therefore expensive manufacturing techniques for both the door piston which is engaged with the pressure piston, and for the pressure piston itself. A complicating factor is that the pressure piston, in addition to the mating surface with the door piston, has two additional mating surfaces, corresponding to which there are two aligned mating surfaces on the housing. These requirements also significantly increase the manufacturing costs.
Finally, the door closer of the known art has a centrally located slide which functions as a switched valve and can be displaced axially both in the door piston and in the pressure piston, and is installed in a hydraulically tight manner. As a result, the diameter tolerances are cumulative, which sets extremely high requirements for precision in the manufacture of such a door closer.
The primary disadvantage, however, is that a large number of pressure or compression chambers are required, all of which must be sealed off from one another and some of which must be in hydraulic communication with one another by means of a complicated system of channels, which means that the desired closing moment characteristic is greatly affected by the temperature--in cold weather in particular. The door closer of the known art also relies heavily on the skill of the assembly and installation personnel, because the hydraulically active cylinder surfaces which are engaged with one another can easily be damaged when the door piston and the pressure piston are assembled to one another, along with the slide which runs through both of them.